V O L U M E 2 1 , NO. 1, J A N U A R Y 1 9 4 9
29
(64) Imhoff, C. E., andBurkardt, L. A, Power, 86, 64 (1942). (65) “International Tables for Determination of Crystal Structures,” Vol. 11, Kew York, Chemical Catalog Co., 1935. (66) Kaufman, H . S., and Fankuchen, I.,unpublished work. 167) Klun. H. P , Alexander. L.. AXAI..CHEM.. 20. 807 (1948). (68) Klug, H. P., Alexander, L., and Iiuminer; E., ‘ J . I n d . Hug. Toricol., 30, 166 (1948). (69) Kronberg, 11.L., reported at meeting of Am. Soc. X-Ray and Electron Diffraction, Gibson Island, Md., 1944. (70) Lanee, J. J. de, and Houtman, J. P. W., Rec. trav. chim., 65, 891 (1946). (71) Lipson, H.. IVatiire, 146, 798 (1940). (72) Lonsdale, K., Am. Mineral., 33, 90 (1948). (73) Lonsdale, K., and Smith, H . , J . Sei. Instrtcments, 18, 133 (1941). (74) Lukesh, J. S., Reu. Sci. Instruments. 11, 200 (1940). (75) XLIcCrone, IT. C . , ASAL. CHEDI..20, 274 (1948). (76) XIacEwan, D. M .C., S u t u r e , 154,577 (1944). (77) Marsden, S. S.. Rea. Sei. Instruments. 16, 192 (1945). (78) Matthews, F. W.,and McIntosh, A. D., Can. Chem. Process I n d . , 29, 320 (1946). (79) R.fatt,hews, F. W., and Michell. 6. H., ISD. ENG.CHEM.,A s a ~ . ED.,18, 662 (1946). (80) Jlikheev, V. I., and Dubinilia, V . K.,A n n . i m t . mir~esLeningrad, 13, 1 (1939). (81) Miller, H. C., Proc. Am. Soc. Testing .lfaterials, 43, 1269 (1943). (82) Milligan, W.0..P h y s . Rev., 67, 197 (1945). (83) Milligan, W. O., and Focke, A. B., J . Phys. Chem., 45, 107 (1941). (84) Milligan, IT. O . , and Merten, L.. .I. Phys. Chem., 50, 465 (1946). (85) Milligan, 1%‘. O., and Watt, SI.L., J . P h y s . Colloid Chem., 52, 230 (1948). (86) Muehlhause, C. O., aiid Friednitin, €I., Ret. Sei. Ins?rrime,z?s, 17, 508 (1946). (87) Nagelschmidt, G., J . Sci. Iirstrumeids, 18, 100 (1941). (88) Nagy. R., and Lui. C. K., J . Optical Sac. Am., 37, 37 (1947). (89) Ness, 1%.K., Rev. Sei. Instruments, 17, 344 (1946). (90) Peacock, M. .i.,Trans. R o y . Soc. Curc.. (113.35, 105 (1941). (91) Primak, W.,Kaufinan, II. S., and Kard, K.,J . A m . Chem. Soc., 70, 2043 (1948). (92) Redmond, J. C., A N . ~ LCHEM., . 19, 773 (1947). (93) Robertson, J. M., J . Sei. Instruments. 20, 175 (1943). (94) Rooksby, H. P., Analyst. 70, 166 (1945).
(95) Xooksby, H . P., J . R o y . Soc. Arts.. 90, 673 (1942). (96) Rooksby, H. P., J . Sei. Instruments, 18, No. 5, 84 (1941). (97) Smith, C. S., and Barrett, R. L., J . Applied Phys., 18, 177 (1947). (98) Sof’ina, C.V , and Korovin, V. I., K h i m . Referat. Zhur., 4, No. 3, 67 (1941). (99) Soldate, A . M . , and Noyes, €3. M., ANAL.CHEM.,19, 442 (1947). (100) “Strukturbericht,” Vols. I-YII, photolithoprint, Ann Arbor, M i c h . , Edwards Brothers, 1943. (101) Swami, S. R., and Seshayengar, M., Current Sei., 11, 276 (1942). (102) Switeer, G., and Holmes, R. J., Am. M i n e r a l . , 32, 351 (1947). (103) Taylor, A, “Introduction t o X-Ray Metallograph>-,”London, ChamIan and Hall. 1945. (104) Taylor; A , Phil. -\fag., 35, 632 (1944). (105) Ibid., 35, 638 (1944). (106) Vand, V., J . Applied Phys., 19, 852 (1948). (107) \-an Talkenburg, h.,J r . , and McMurdie, H . F., J . Research .\7atl. Bur. Sthndards, 38, 415 (1947). (108) Wainwright, C., J . Sei. Instruments, 19, 165 (1942). (109) Waite, J. M., Rev. Sei. Instruments, 17, 557 (1946). (110) Walton, G., and Walden, G. H., J . Am. Chem. Soc., 68, 1742 (1946). (111) Ibid., 68, 1750 (1946). (112) Warren, B. E., J . Applied Phys., 12, 374 (1941). (113) Weiser, H. B., Milligan, W.O., andBates, J. B., J . Phys. Chem., 46, 99 (1942). (114) Weissberger, A , , “Physical Methods of Organic Chemistry,” Vo1. I, Chapter on X-Ray Diffraction by I. Fankuchen, Pr’ew York, Interscience Publishers, 1945. (115) Wilchinsky, Z. W., J . Applied Phys., 18, 929 (1947). (116) Wilson, A. J. C., and Lipson, H., Proc. P h y s . Soc., 53, 245 (1941). (117) Wycoff, R. IT. G.. “Cr\-stal Structures,” Section I, New York, Interscience Publishers, 1948. (118) Wycoff, R. IT. G., “Structure of Crystals,” 2nd ed., New York, Reinhold Publishing Corp., 1931. (119) Ibid., Supplement for 1930-34, 1935. (120) Zachariasen, W. H., “Theory of X-Ray Diffraction in Crystals,” New York, John Wiley & Sons, 1945. RECEIVED Xorernber 6, 1948.
EMISSION SPECTROSCOPY WILLLA31 F. MEGGEHS .\-ativnul Bureau of Standards, F’ushington, D . C .
I
K
T H I S article attention is directed t o the principal postwar spectroscopic advances in fundamental research and applications, in so far as these have been published and are known t o the writer. T h e status of fundamental research in spectroscopy was summarized (44) in 1946, a’nd more than 1000 published applications t o spectrochemical analysis were indexed and abstracted (53) for the years 1940 t o 1945 inclusive. TERM ANALYSIS
Structural analysis and quantum interpretation of atomic emission spectra progressed spectacularly from 1922 t o 1940, when World War I1 interrupted it. Since the war this phase of spectroscopic research is gradually being revived, as evidenced by the following publications. T h e sp3 6s state of carbon atonis was thought to be important for the theory of chemical binding energies of carbon compounds, but its value was unknown until Shenstone (56) produced evidence that it is 33,735.2 cm.-l above the groundostates2p23P. T h e o b srrvation of transitions (2965 and 2967 A.) between these two states implies t h a t 5S is not a metastable state and should not therefore enter in t h a t role in thermochemical theory. New lines and terms of the first spectrum of fluorine have been reported by LitlCn (40). Rrccnt contributions t o the analysis of alkali spectra have come
from Meissner et a!., who employed excited atomic beam3 and interferometers t o resolve some of the 2D terms of lithium (48). A Anal, practically complete compilation and analysis of the first spectrum of copper has been published by Shenstone (55). It appears t h a t the copper spectrum exhibits most of the peculiaiities t h a t can be found in atomic spectra. For instance, it has a radically perturbed series, and more examples of auto-ionization than all other known spectra, and is the only example of a co111plex series converging toward a limit more complex than a doublet. Of its 174 identified rnergy levels, 110 lie above the level of easiest ionization. The preliminary analysis of the first spect r u m of rhenium given by Meggers in 1931 has been extended b v Klinkenberg (S8), who increased the number of classified lines from 500 t o 1624. Spectra of the rare earth tvpe are still t h e outstanding unfinished business of complex spectrum analysis. T h e only results for elements containing electrons of 4f type, published I Xdrr b y Schuurmans (51) a n d since the war, are those for N ~and for YbxI by Meggers (45). With the aid of the Zeeman effect Kiess et al. (34) analyzed the first spectrum of uranium. This was t h e first instance in ivhich the 5f electron was positively identified in the ground state of a neutral atom; it appears t h a t the normal electron configuration of uranium is 5j36d17s2. Similar results for the UI spectrum have been published by Schuurmans et al. ( j Z ) ,
30
ANALYTICAL CHEMISTRY
who also reported extensive data for the UIIspectrum. Spectroscopic evidence for the electron configurations of elements containing 4f- and 5f-type electrons was recently summarized (47). Progress in the description and analysis of higher stage spectra of light elements was reported by Soderqvist (59) for NaIv, Xav, Navr, Mgv-, M ~ v I and , hlgrI1, and by Ferner (24) for Alv to .41x1, SivI to SixII, and SVIIto SIX. A large amount of unpublished information on the structure of atomic and ionic spectra will be found in a compilation (49) of atomic energy levels which will be issued in several volumes by the National Bureau of Standards. Volume I contains data on ionization potentials, electron configurations, spectral terms, quantum numbers, and magnetic splitting factors (where known) for 205 spectra characteristic of the first 23 atomic numbers, lH to 2aV.
ZEERZAN EFFECT
The most effective aid in the interpretation of spectra is line splitting and polarization in magnetic fields. New observations have been published for Xdr, YdIr, GdI, and ThrI by Klinkenberg (ST),for Sell, and UI, and U I I by van den Bosch ( 7 ) , and for X I and 01by Kiess and Shortley (36). Incidentally, the latter are the lightest elements for which magnetic splitting factors have been determined. ISOTOPE SHIFTS
Measurement of the isotope shift of the red line (6678 A.) of He3 relative to He4 x a s reported (2) in agreement with the theoretical value. No satisfactory theory exists for isotope shifts of heavier elements such as have been observed for ?;dl421 144, 116, 148, 160 (361, Gdl58, 168, 160 ( S T ) , and UZ3312 3 6 ~ 23* (fa). Irregularities among isotope shifts are a challenge t o the theoretical physicist; they must be accounted for by a satisfactory theory of nuclear interactions with optical electrons. HYPERFINE STRUCTURE
The interaction of optical electrons with atomic nuclei possessing angular momenta results in hyperfine structures of spectral lines, and under favorable circumstances the resolved hyperfine structure yields quantitative results for the mechanical, magnetic, and quadrupole moments of the nuclei. A spin of 9/2
- unit
(:T
)
for Cb03has been definitely established (43). Partial resolution of a hyperfine pattern indicates (1)a spin of 5/2 (or possibly 712) for V 3 5 , and from the fact that lines of Kp237 exhibit a mayimum of ais components it is concluded (62) that this nucleus has a spin of 5/2. From measurements of alternating intensities in band spectra of carbon compounds, Jenkins (53)has shown conclusively that the spin of CI3 ii; 112 and of C14is 0. If this review were not confincd to conventional emijsion spectroscopy, mention could be made of spectacular and important measurements of nuclear moments by means of magnetic resonance and by microwave techniques derived from the development of radar during World War 11. These measurements have been made not only on chemical elements (H, D, T, He, C, S , K, C1, Br, Cu, Ga, etc.) but also on elementary particles (electron, proton, neutron). NEW ELEMENTS
Stypendous neutron flux density in chain-reacting uranium piles has resulted in the manufacture, either by transmutation or by fission, of tangible amounts of artificial isotopes or new elements, thus expanding the domain of spectroscopy. Publication of spectroscopic data on these artificial elements is still very meager, but the following may be cited. The K-x-ray spectra of 43Tc and of "Pm have been deslribed (10, 11). Hg108,produced by transmuting Au'Q', emits superlatively sharp spectral lines whose wave lengths suggest themsrlves
as the ultimate standard of length (46). The spectra of transuranic elements have not been ofully revealed (or studied), but for identificatio; one line (4164.5 A,) characteristic of 93Np and one line (3709.1 A.) characteristic of 91Puhave been disclosed (26). A large program of stable-isotope separations a t Oak Ridge has further extended the possibilities of spectroscopic research, especially in the study of isotope shifts and hyperfine structures. I n fact, the number of possible and profitable problems in fundamental spectroscopy is a t present many times greater than the number of persons actually engaged with them. SPECTROCHEMICAL ANALYSIS
Whereas practically all postwar published research in fundamental spectroscopy has been cited here, to do likewise for emission spectroscopy applied to spectrochemical analysis would entail a bibliography of more t,han 400 papers. The majority of these deal with quantitative analysis of metal alloys, in which field spectrography had already displaced classical chemicah methods, except for the determination of gases, sulfur, and carbon. The possibility of determining carbon in steel by a spectrographic method using a simple condensed spark has been investigated by Garton (26). Techniques for the spectrographic determination of boron in steel were developed (18, 41) as a wartime problem. The colossal size of the metallurgical industry and the necessity of adequate composition control of complex alloys have justified the development of expensive source units and direct-reading spectromct,ers. The latter eliminate photographic recording, processing, and measuring by employing a s detect,ors electron-multiplier phototubes that charge condensers, which then actuate mechanisms calibrated to indicate per cent composition. Such direct-reading instruments and t,heir use in t h e spectrochemical analysis of steels have been described in some detail (15, SO). Similar applications of direct-reading instruments to analysis of nonferrous alloys have aljo been made, for example, to magnesium alloys (50) and to aluminum alloys (4)in which more than 100,000 element analFsea per month are possible. Direct reading of 20 elements in light alloys has been described (6). Application of Geiger-Muller counters in the direct deterniination of phosphorus in steel should also be mentioned (9, 28) : likewise, spectrochemical analysis lrith the oscillograph (19). Yotahle progress has been made in the spectrochemical analysis of lubricating oil additives, additive lubricants, and gasolines ( l 4 ) , of minor constituents in portland cement ( S f ) , of rare earth elements (22, 23) and of ceramic and other nonmetallic materials (52, 64). Two papers on a method of analysis based on photographic line widths (17 , 20) claim that this method is independent of exposure time, photographic development, and self-reversal, and is, therefore, more precise than the photographic-density method. The manufacture of atomic bombs was responsible for the development of a carrier-distillation method of analyzing uranium for 33 volatile impurities (64),and a copper-spark method of analyzing plutonium for 61 other elements (26). T h a t applied spectroscopy can give warning of toxic elements is illustrated in the spectrographic determination of beryllium in biological material and in air (16), and in the development of a rapid mobile analyzer for minute amounts of lead in air ( 5 ) . Recent attempts to detect and determine gases spectrographically are solely represented by experiments with halogens excited either by ultra-highfrequency electric fields (27) or in hollow cathode discharges (42). There appear to be only two recent examples of isotopic analysis by means of atomic spectra; these are the determination of deuterium in hydrogen (61) and concentrations of 2 3 5 * 238 in uranium samples (12). Efforts further to improve the accuracy of spectrochemical determinations have brought forth other modifications of the classical spectroscopic arc and spark sources: a condensed arc source ( 6 7 ) ,a combination arc-spark source ( I S ) , a combination P
3
1
V O L U M E 21, NO. 1, J A N U A R Y 1 9 4 9 spark-arc source ($9), and B general purpose source providing a simple condensed spark, a direct current arc, and intermediates (63). The low-voltage controlled alternating current arc is claimed to be an improved source (8) and a study concerning characteristics of the high-voltage alternating current arc has been reported ( 6 ) . An air-interrupter type of spark source has also been described ($1). Despite a reputation for instability, the direct current arc has not been discarded, and the reasons for its continued use are not far to seek. Compared with elaborate and expensive controlled sparks, high-voltage alternating current arcs, and multisource units, the direct current arc is absurdly simple and cheap; it requires only a n electrode holder and a rheostat. Because of a large power consumption and high temperature the direct current arc is most efficient in vaporizing and exciting refractory materials; recent applications t o the spectrochemical determination of the major constituents of minerals and rocks (39), and to quantitative analysis of ceramic and other nonmetallic samples (32) and of rare earth oxides ( l l , d S ) have been reported. Because the direct current arc is the least ionizing of the electrical sources, it favors the excitation of neutral atoms whose strongwt lines occur in the observed range of spectrum, and consequently it is naturally superior in detectability of trace elements; for this reason it is necessarily used in the spectrochemical analysis of high-purity materials (58). The main cause of poor reproducibility usually asssociated with the direct current arc source has been traced to fractional distillation. Strock and Heggen (60) have shown t h a t reproducibility is greatly improved by employing an internal. standard with excitation properties comparable with those of the analysis lines. Fassel (26) has obtained high precision by nearly ideal internalstandard compensation of excitation variables; if the internal standard and analysis elements have similar physical properties, the intensity ratios of line pairs are independent of current, weight of charge, per cent of graphite, depth of cavity, length, and region of the analytical gap. Satisfactory precision may be expected from any spectroscopic source, provided the necessary cbnditions of the internal-standard principle are fulfilled. Perhaps too much emphasis has been placed on electrical apparatus and circuits and not enough on the physical properties of the chemical elements to be detected or determined. Unfortunately, the melting and boiling points of some elements are still unknown or very uncertain. Liken-ise, the excitation characteristics and relative intensities of many spectral lines are unknown. In conclusion, attention is called to the present disparity between fundamental and applied spectroscopy-for every research spectroscopist there are now hundreds of spectrographers, and for one paper on fundamental spectroscopy there are at leait ten on applications. Publication of a n international journal of applied spectroscopy, Spectrochirnica Acta, founded in 1939 and suspended in 1944, was resumed in 1947, and in this countrv a half dozen or more societies of applied spectroscopy have been organized, a t least one of which is publishing a Soczety j o r Applied Spectroscopy Bulletin. S o one can find fault with this amazing activity in applied spectroscopy, but, rememhering that progress rests upon new knowledge, it is extremely important to attract more investigators to fundamental reiearch. LITERATURE CITED
Anderson, 0. E., and White H. E., Phys. Rev., 71, 911 (1947). Andrew, A., and Carter, W. W., Ibid., 74, 838 (1948). Aughey, H., J . Optical SOC.Am., in press. Blair, T. S., Iron Age, 160, 65-7, 135 (1947). Boettner, E. A., and Tufts, C. F., J . Optical SOC.Am., 37, 192-8 (1947). Bonsack, W., Metal Progress, 52, 975-8 (1947). Bosch, J. C. van den, Physica, 14, 249-59 (1948) ; dissertation, Amsterdam, 1948. Brando, C., and Clayton, H . R., J . Soc. Chem. Ind., 66, 259-67 (1947).
31 (9) Bryan, F. R., and Nahstoll, G. A . , J . Optical SOC. Am., 38, 510-17 (1948). (10) Burkhart, L. E., Peed, W.F., and Saunders, B. G., Phys. Rev., 73, 347 (1948). (11) Burkhart, L. E., Peed, W.F., and Spitaer, E. J., Y-173, Oak Ridge, Tenn. ( M a y 24, 1945). (12) Burkhart, L. E., Stukenbroeker, G., and Adams, S., Atomic Energy Commission, D-2001 (1948). (13) Caldecourt, 1’. J., and Saunderson, J . L., J . Optical SOC.Am., 36, 99-102 (1946). (14) Calkins, L. E., and White, M. M.,Proc. Am. Petroleum Inst., 26 (111),80-90 (1946). (15) Carpenter, R. O’B., Du Bois, E., and Sterner, J., J . Optical SOC. Am., 37, 707-13 (1947); in press. (16) Cholak, J., and Hubbard, D. A I , , i 4 ~CHEM., ~ ~ 20, . 73-6 (1948). (17) Coheur, P., J . Optical SOC.Am., 36, 498-500 (1946). (18) Corliss, C. H., and Scribner. B. F., J . Research *Vatl.Bur. Standards, 36,351-64 (1948). (19) Dieke, G. H., and Crosswhite, H. M., J . Optical SOC.Am., 36, 192-5 (1946). (20) Eastmond, E. J., and Williams, B. E., Ibid., 38, 800-3 (1948). (21) Enns, J. H., and Wolfe, R. 8., J. Optical SOC. Am., 37, 519 (1947) ; 38 (Oct. 23, 1948). (22) Fassel, V. A., J. Optical Soc. Am., in press. (23) Fassel, V. A , , and Wilhelm, H . A , , Ibid., 38, 518-26 (1945). (24) Ferner, E., Arkiv. Mat. Astron. Fysik,36A, No. 1 (1948). (25) Fred, M., Nachtrieb, N. H., and Tomkins, F. S., J . Optical SOC. Am., 37,279-88 (1947). (26) Garton, F. W. J., Spectrochim. Acta, 3, 68-85 (1947). (27) Gatterer, A., and Frodl, V., Ricerche Spettroscop., 1, 201-44 (1946); Spectrochim. Acta, 3, 214-32 (1948). (28) Hanau, R., and Wolfe, R. A , , J . Optical Soc. Am., 38, 377-83 (1948). (29) Hasler, M.F., and Kemp, J. W., Ibid., in press. (30) Hasler, M. R., Kemp, J. W., and Dietert, H. W.,A.S.T.M. Bull. 139 (1946); J . Optical SOC.Am., 38, 789-99 (1948). (31) Hela, A W., and Scribner, B. F., J . Research S a t l . Bur. Standards, 38,439-47 (1947). (32) Jaycox, E. K., J . Optical SOC.-4m., 37, 162-5 (1947). , Phys. Rev., 74, 355-63 (1948). (34) Kiess, C. C., Humphreys, C. J., and Laun, D . D., J . Research .Tall. Bur. Standards, 37, 1-16 (1946). (35) Kiess, C. C., and Shortley, G., Ibid., in press. (36) Klinkenberg, P. F. A . , Physica, 11, 327-38 (1945). (37) Ibid., 12, 33-48 (1946). (38) Ibid., 13, 581-604 (1947); 14, 269-84 (1945). (39) Kvalheim, J . Optical SOC.Am., 37, 585-92 (1947). (40) LidBn, K., Arkiv. Mat. Astron. Fysiic, 35A, No. 24, (1948). (41) Lutsenko, .I.T’., and Sorokina, N. N., Zavodskaya Lab., 12, 57476 (1946). (42) McKaliy, J . R., Harrison, G. K., and Rowe, E., J . Optical SOC. Am., 37, 93-8 (1947). (43) Rfeeks, W.W., and Fisher, R. A , Phys. Rev., 72, 451-5 (1947). (44) Meggers, W.F., J . Optical Soc. Am., 36, 431-48 (1946). (45) Ibid., 37, 988-9 (1947). (46) Ibid., 38, 7-14 (1948). (47) Meggers, 11’. F., Science, 105, 514-16 (1947). (45) Meissner, I
